Mr. Xiongtao Zhao Profile

Xiongtao Zhao

at Nanjing Univ of Science & Technology

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Publications (2)

Proceedings Article | 8 November 2024 Paper

Thermal resistance investigate of copper-copper interface based on femtosecond laser periodic microstructure

Ning Wang, Zihan Liu, Hualong Zhao, Xiongtao Zhao, Yupeng Zhang

Proceedings Volume 13234, 132340X (2024) https://doi.org/10.1117/12.3040482

KEYWORDS: Interfaces, Composites, Resistance, Copper, Laser microstructuring, Liquids, Laser processing, Femtosecond phenomena, Metals

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With the progress of national defense science and technology, the thermal effect of components in aerospace technology has greatly hindered the operation of devices. In order to solve the problem of high interface thermal resistance between materials, a new method of femtosecond processing combined with thermal interface materials was proposed to reduce interface thermal resistance. By using the high-efficiency positioning response method and the non-material selectivity and low thermal effect of femtosecond laser, the micro-structure with low roughness is precisely machined on the surface of copper based on the laser five-axis machining system, and the internal structural roughness, depth and width of the micro-structure are characterized. Then the surface is covered with thermal interface materials to achieve the purpose of reducing the interface thermal resistance between materials. At the same time, the effect of microstructure on interface thermal resistance is simulated with simulation software. A uniform array structure was obtained on the surface of copper substrate with a roughness less than 0.3μm, and the measured linear roughness of the microstructure was 0.23μm, which was consistent with the surface roughness of copper. Firstly, in order to verify that the surface heat conduction efficiency of the material with a microstructure surface is higher, the heat transfer time of the composite substrate with a microstructure is 0.0073s after simulation, which is faster than that of the composite substrate without a microstructure. Then, the thermal conductivity of the composite substrate with low roughness is 355 W·m^-1 ·K^-1, while that of the composite substrate with high roughness is 325 W·m^-1 ·K^-1 . Through the ultrafine processing, the heat transfer efficiency of the prepared composite substrate is increased by 17%, and the heat transfer efficiency is higher with lower roughness, which provides a research basis for high energy consumption devices.

Proceedings Article | 19 February 2018 Paper

Nano- and micro-structuring of fused silica using time-delay adjustable double flash ns-laser radiation

Pierre Lorenz, Xiongtao Zhao, Martin Ehrhardt, Igor Zagoranskiy, Klaus Zimmer, Bing Han

Proceedings Volume 10520, 105201K (2018) https://doi.org/10.1117/12.2288294

KEYWORDS: Pulsed laser operation, Silica, Metals, Etching, Molybdenum, Dielectrics, Liquids, Nanostructuring, Plasma, Chromium

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Large area, high speed, nanopatterning of surfaces by laser ablation is challenging due to the required high accuracy of the optical and mechanical systems fulfilling the precision of nanopatterning process. Utilization of self-organization approaches can provide an alternative decoupling spot precision and field of machining. The laser-induced front side etching (LIFE) and laser-induced back side dry etching (LIBDE) of fused silica were studied using single and double flash nanosecond laser pulses with a wavelength of 532 nm where the time delay ∆τ of the double flash laser pulses was adjusted from ∼50 ns to ∼10 μs. The fused silica can be etched at both processes assisted by a 10 nm chromium layer where the etching depth ∆z at single flash laser pulses is linear to the laser fluence and independent on the number of laser pulses, from 2 to 12 J/cm², it is ∆z = δ_LIFE/LIBDE ⋅ Φ with δ_LIFE ∼ 16 nm/(J/cm²) and δ_LIBDE ∼ 5.2 nm/(J/cm²) ∼ 3 ⋅ δ_LIFE. At double flash laser pulses, the ∆z is dependent on the time delay ∆τ of the laser pulses and the ∆z slightly increased at decreasing ∆τ. Furthermore, the surface nanostructuring of fused silica using IPSM-LIFE (LIFE using in-situ pre-structured metal layer) method with a single double flash laser pulse was tested. The first pulse of the double flash results in a melting of the metal layer. The surface tension of the liquid metal layer tends in a droplet formation process and dewetting process, respectively. If the liquid phase life time ∆t_LF is smaller than the droplet formation time the metal can be "frozen" in an intermediated state like metal bare structures. The second laser treatment results in a evaporation of the metal and in a partial evaporation and melting of the fused silica surface, where the resultant structures in the fused silica surface are dependent on the lateral geometry of the pre-structured metal layer. A successful IPSM-LIFE structuring could be achieved assisted by a 20 nm molybdenum layer at ∆τ ≥ 174 ns. That path the way for the high speed ultra-fast nanostructuring of dielectric surfaces by self-organizing processes. The different surface structures were analyzed by scanning electron microscopy (SEM) and white light interferometry (WLI).

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